TY - JOUR
T1 - Considerable enhancement of emission yields of [Au(CN)2-] oligomers in aqueous solutions by coexisting cations
AU - Wakabayashi, Ryo
AU - Maeba, Junichi
AU - Nozaki, Koichi
AU - Iwamura, Munetaka
N1 - Publisher Copyright:
© 2016 American Chemical Society.
PY - 2016/8/1
Y1 - 2016/8/1
N2 - The photophysical properties of [Au(CN)2-] oligomers in aqueous solutions were investigated as functions of coexisting cations as well as the viscosity and temperature of solutions. A solution of [Au(CN)2-] in the concentration range of 0.03-0.2 mol/dm3 exhibited emission peaks at 460-480 nm because of the presence of oligomers larger than trimers. Although the emission yields (βem) of K[Au(CN)2] solutions were <1%, it considerably increased to 43% when 1.0 mol/dm3 tetraethylammonium chloride (Et4NCl) was added. The lifetimes of the main emission bands were also significantly varied with additional salts, e.g., KCl, 15 ns; Et4NCl, 520 ns. The time-resolved emission measurements of [Au(CN)2-] in a water/glycerol mixture indicated that the lifetimes were almost directly proportional to the inverse of the viscosity of the solution. On the other hand, the intrinsic lifetimes of dimers and trimers with weak emission in shorter wavelength regions were very short and independent of the viscosity of the solutions and coexisting cations (dimer, ∼25 ps; trimer, ∼2 ns). These results indicated that the deactivation of the excited-state [Au(CN)2-]n oligomers (n ≥ 4) was dominated by the dissociation of the oligomers to a shorter species (dimer or trimer). The hydrophobic interactions between tetraalkylammonium cations and CN ligands remarkably stabilized the larger oligomers and suppressed the dissociation of the excited-state oligomers, which enhanced the emission yield of the oligomers. This work provides a new method of "exciplex tuning" by changing the environment of excited-state [Au(CN)2-]n oligomers.
AB - The photophysical properties of [Au(CN)2-] oligomers in aqueous solutions were investigated as functions of coexisting cations as well as the viscosity and temperature of solutions. A solution of [Au(CN)2-] in the concentration range of 0.03-0.2 mol/dm3 exhibited emission peaks at 460-480 nm because of the presence of oligomers larger than trimers. Although the emission yields (βem) of K[Au(CN)2] solutions were <1%, it considerably increased to 43% when 1.0 mol/dm3 tetraethylammonium chloride (Et4NCl) was added. The lifetimes of the main emission bands were also significantly varied with additional salts, e.g., KCl, 15 ns; Et4NCl, 520 ns. The time-resolved emission measurements of [Au(CN)2-] in a water/glycerol mixture indicated that the lifetimes were almost directly proportional to the inverse of the viscosity of the solution. On the other hand, the intrinsic lifetimes of dimers and trimers with weak emission in shorter wavelength regions were very short and independent of the viscosity of the solutions and coexisting cations (dimer, ∼25 ps; trimer, ∼2 ns). These results indicated that the deactivation of the excited-state [Au(CN)2-]n oligomers (n ≥ 4) was dominated by the dissociation of the oligomers to a shorter species (dimer or trimer). The hydrophobic interactions between tetraalkylammonium cations and CN ligands remarkably stabilized the larger oligomers and suppressed the dissociation of the excited-state oligomers, which enhanced the emission yield of the oligomers. This work provides a new method of "exciplex tuning" by changing the environment of excited-state [Au(CN)2-]n oligomers.
UR - http://www.scopus.com/inward/record.url?scp=84979987779&partnerID=8YFLogxK
U2 - 10.1021/acs.inorgchem.6b01205
DO - 10.1021/acs.inorgchem.6b01205
M3 - 学術論文
C2 - 27391559
AN - SCOPUS:84979987779
SN - 0020-1669
VL - 55
SP - 7739
EP - 7746
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 15
ER -